1. Field of the Invention
The present invention generally relates to the production of X-rays and, more particularly, to a method of and arrangement for producing X-rays by the Compton scattering effect in a desired frequency range suitable for medical diagnostic and therapeutic, or industrial testing, purposes. Still more particularly, this invention relates to a novel method of and apparatus for electronically steering an X-ray beam, as well as to a method of and apparatus for X-raying an object with a narrow band frequency characteristic.
2. Description of the Prior Art
Conventionally, X-rays are generated for medical diagnostic purposes by using a cathode tube, wherein a stream of electrons is directed towards a metal plate for impingement thereon, to thereby cause the metal material to emit radiation in the X-ray range which, for diagnostic purposes, lies in the range from about 20 Kev. to 100 Kev. Since this process depends on the excitation of the shell electrons of the metal and on spontaneous level change within the atom shell envelope, accompanied by sudden energy release in the form of X-rays, the characteristics of individual X-ray photons cannot be determined. The conventional X-ray tube emits a highly divergent X-ray beam with a distribution of the frequencies or energy levels of the photons in the X-ray beam over a very wide range. To protect the operating personnel and/or the patient from undue exposure to X-rays, it is necessary to shield or mask the X-ray apparatus, so that the issuing beam will only cover the desired area to be X-rayed. Mechanical shutters are used to control the emission angle.
The use of a conventional X-ray tube for medical diagnostic purposes is far from an ideal situation, since the shielding is rarely perfect and, moreover, only a fraction of the produced X-rays is available for the desired use. The situation is further aggravated by the fact that the X-ray beam is distributed over a very wide X-ray spectral range, so that the object being X-rayed, be it an article to be tested, examined or analyzed, or a portion of a body of a patient to be examined or subjected to radiation therapy, is exposed not only to the X-ray radiation of the most beneficial energy level, but also to X-rays having energy levels outside the beneficial range. Thus, the exposure of the object to X-rays or, in other words, the dosage of the X-ray radiation, is far in excess of the necessary level since, in order to achieve the desired dosage of the beneficial X-ray energy level, the object is simultaneously exposed to a substantial dosage of X-ray radiation outside the beneficial range.
For radiation therapy purposes, X-rays in the range from about 10 Kev to about 250 Kev are used and, conventionally, for the higher energy range, a linear accelerator may be used to accelerate a stream of electrons against a metal plate to cause X-ray emission. However, the very same drawbacks described above are still present, because the issuing high energy X-rays also have a wide angle beam and a broad band frequency characteristic.
For elemental analysis purposes, polarized X-rays are desired. Conventionally, polarized X-rays are produced by passing unpolarized X-rays through materials, such as graphite. However, this is a very inefficient process. In medical radiography, polarized X-rays have never, to our knowledge, been used and, hence, their potential utility remains to be explored.
In the field of physics research, large electron storage rings which accelerate electrons around a closed loop are utilized to generate polarized X-rays as a byproduct of the electron acceleration and deceleration process. However, these large electron storage rings are massive installations, are present at only a few locations around the world, and are not practical for use in medical or industrial applications.
Still another drawback of conventional X-ray apparatus is that the X-ray beam itself has never been electronically steered. It is well known that X-ray scanning of a patient is a highly desirable medical technique and, hence, the conventional techniques to accomplish scanning are to mechanically move the patient, or to mechanically move the X-ray tube itself, or to mechanically move the exit shutter of the X-ray apparatus. In some hospitals, there are huge X-ray machines which place the patient on a table, and move the patient in a desired direction. Also, the patient can remain stationary, and the X-ray machine can move around the patient. All of these prior art techniques are very cumbersome and unwieldy and, most importantly, are slow, i.e. on the order of 15-20 seconds or more and, hence, patient movement can cause X-ray blur.
It is also known in the field of nuclear physics research to use the Compton backward scattering effect for producing gamma rays, i.e. high energy photons which lie in the multi-Mev to Gev region. Briefly summarized, the Compton effect is characterized as follows: An incoming photon supplied by a light source, such as a laser, is collided with an incoming electron supplied by an electron accelerator. The result of the collision is that the electron loses energy, and the photon gains energy. The outgoing or deflected photons have a very high energy level, and typically are in the gamma-ray range identified above. The Compton effect, to the best of our knowledge, has never been used to generate X-rays for bio-medical and industrial investigations.